At the heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes at least one coil, a write pole and one or more return poles. When a current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the write pole, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic disk, thereby recording a bit of data. The write field, then, travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head.
A magnetoresistive sensor such as a Giant Magnetoresistance (GMR) sensor or a Tunnelling Magnetoresistance (TMR) sensor can be employed to read a magnetic signal from the magnetic media. The magnetoresistive sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the adjacent magnetic media.
As the need for data density increases there is an ever present need to decrease the bit length in order to increase the linear data density. With regard to the magnetic head, this means reducing the shield-to-shield (SS) spacing of the read head (i.e. the read gap thickness). However, physical limitations as well as manufacturing limitations have constrained the amount by which the gap thickness of the magnetic read head can be reduced. For example current magnetic sensors require a pinned layer structure that includes two anti-parallel coupled magnetic layers with a non-magnetic layer sandwiched between them and a relatively thick antiferromagnetic (AFM) material layer to pin one of the magnetic layers. This pinned layer structure consumes a large amount of the gap budget and greatly impedes efforts to reduce the gap thickness (and consequently the bit length) of the recording system. Therefore, there remains a need for magnetic sensor design that can provide the reduced gap thickness needed for future magnetic recording requirements.